JP2698089B2 - Control method of image forming apparatus - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for controlling an image forming apparatus.

2. Description of the Related Art In an image forming apparatus that forms an electrostatic latent image on a photoconductor, visualizes the image with a developer, and transfers the visible image to transfer paper, the number of image formation increases because the photoconductor is used repeatedly. Accordingly, the photoreceptor becomes fatigued, and the quality of the image on the transfer paper deteriorates. As a method for preventing the deterioration of image quality due to the photoreceptor fatigue, for example, in Japanese Patent Application Laid-Open No. 53-133683, an electrostatic latent image is formed on at least a part of the photoreceptor by a reference original having a predetermined density portion, It has been proposed to control the charge amount and the exposure amount based on the detected value so that the electrostatic contrast is kept constant.

This method takes advantage of the fact that when the charge amount is increased, the amount of increase in the latent image potential in the black portion of the reference original is greater than the amount of increase in the latent image potential in the white portion. as the difference V _D -V _L of the latent image potential V _L (so-called dynamic range) is constant with respect to _D and the white portion, so as to control the charge quantity to adjust the charger voltage to charge the photosensitive member However, in such a control method, there is a problem that the potential characteristics of the photoreceptor change, and the sharpness and gradation of the image fluctuate significantly.

Further, Japanese Patent Application Laid-Open No. 53-98834 discloses that a light portion charge and a dark portion charge of a photoreceptor are detected, and the exposure amount is controlled by the light portion charge and the primary charge is controlled by the dark portion charge. In this case, the exposure control is performed by blinking an exposure lamp having a light intensity approximately equal to the light intensity at the time of document irradiation. Normally, the sensitivity of the photoconductor is not linear,
The larger the light amount, the lower the sensitivity, and in this conventional method, the exposure amount becomes considerably large, so that the sharpness of image quality, low contrast reproducibility, and deterioration of gradation are caused. In addition, since the detection is performed at two points, that is, a bright portion and a dark portion, there is a problem in that when fatigue starts to occur on the photoconductor, control for forming a latent image similar to that when there is no fatigue cannot be performed.

It is an object of the present invention to provide a method for controlling an image forming apparatus capable of solving the above-mentioned conventional problems, obtaining a stable latent image potential even when the photosensitive member is fatigued, and maintaining stable and good image quality. It is intended to be.

Configuration The present invention, in order to achieve the above object, on one surface, while detecting the latent image potential in each color portion of the reference latent image having a black portion and a white portion formed on the photoreceptor, Detecting the residual potential of the photoreceptor, and based on the initial latent image potential of the black part and the detected residual potential, in order to set the difference between the latent image potentials of the black part and the white part to a predetermined constant value. A target potential is set, and the detected latent image potential of the black portion is moved to the target potential, and based on the initial latent image potential of the white portion and the detected residual potential, the initial latent image potential of the black portion is set. From the initial latent image potential of the white portion by the same amount as the shift amount from the target potential to the target potential.
And controlling the electrostatic latent image forming means so as to move the detected latent image potential of the white portion to the second target potential, thereby controlling the image forming apparatus. It is preferable to control the developing bias voltage based on the detected residual potential.

In another aspect, while detecting the latent image potential in each color portion of the reference latent image having a black portion and a white portion formed on the photoreceptor, detecting the residual potential of the photoreceptor, And controlling the developing bias voltage from the difference between the initial residual potential and the detected residual potential to make the difference between the latent image potentials of the black part and the white part a predetermined constant value, based on the residual potential difference. From the difference between the initial latent image potential of the black portion and the detected black latent image potential and the difference between the initial latent image potential of the white portion and the detected white latent image potential, the charge amount and the exposure amount on the photoreceptor are respectively determined. The image forming apparatus is controlled by both steps of controlling.

In still another aspect, detecting the residual potential of the photoconductor, detecting the latent image potential at each density of the reference latent image having a black portion and a white portion formed on the photoconductor,
The developing bias voltage is controlled so as to superimpose and apply an increase in the detected residual potential from the previous detection, and the difference between the latent image potentials of the black portion and the white portion is set to a predetermined constant value. Therefore, based on the increase in the residual potential and the difference between the black latent image potential and the detected potential of the black latent image and the difference between the initial latent image potential of the white portion and the detected potential of the white latent image, the charging grid voltage And controlling the exposure lamp voltage to control the image forming apparatus.

The configuration and operation of the present invention will be described in detail based on an embodiment shown in the drawings.

In FIG. 1 showing a copying machine as an example of an image forming apparatus to which the present invention can be applied, reference numeral 1 denotes a photosensitive drum which rotates in the direction of an arrow. 2 is a charger, 3 is an exposure unit, 4 is an eraser, 5 is a development unit, 6 is a transfer charger,
Reference numeral 7 denotes a separation charger, 8 denotes a cleaning device, and 9 denotes a static elimination lamp, which constitute a known electrostatic copying machine. The original placed on the contact glass 10 is scanned by the exposure lamp 11, and the reflected light from the original is reflected on mirrors 12, 13, and
An image is formed on the photosensitive drum 1 in the exposure unit 3 by the imaging lens 14 and the imaging lens 15.

The photoreceptor drum 1, for example, a Se photoreceptor is uniformly positively charged, for example, in the dark by the charger 2 in the dark, and an exposure unit 3 forms an electrostatic latent image corresponding to a document image. At this time, eraser 4
As a result, the charges charged outside the image area are erased.
This is called a latent image forming step.

In the developing unit 5, a black powder called a toner of a developer adheres to a portion corresponding to a black portion of the image according to a developing bias voltage and a potential of a photoconductor surface potential of the black portion, thereby forming a latent image. The toner does not adhere to the white part because the potential is smaller than that of the black part. This is called a visualization step.

Assuming that the surface potential of the photoconductor is V _S and the developing bias voltage is V _B , the amount M of toner adhering to the photoconductor drum is generally M =
It is represented by V _S −V _B.

Generally, from the viewpoint of copy quality, V _S of a portion having a high latent image potential such as the potential V _D of a black portion is represented by image density, and V _{S of a} portion having a low latent image potential such as a potential V _L of a white portion. The quality is evaluated in a manner called rash or background stain.

As is apparent from the equation relates to a toner adhesion amount M of the image density by increasing the developing bias potential V _B decreases and scumming is reduced, but scumming by increasing the surface potential V _S of the photosensitive member is not changed, The image density will increase.

After the transfer, the photosensitive drum is cleaned by a cleaning device 8 to remove a small amount of remaining toner.
, So that the latent image on the photosensitive drum has a uniform potential. The light amount of the charge removing lamp 9 is a light intensity that can sufficiently remove the charge even if the sensitivity of the photosensitive drum is deteriorated.

The amount of light of the eraser 4 in the latent image forming step is, for example, stronger than that of a portion irradiated with light from the exposure unit 3, the neutralizing lamp 9, and the like, and is twice the amount of light necessary to lower the potential on the photosensitive drum 1 most. And This is set in consideration of the deterioration with time of the eraser 4 and a slight margin, and is understood as a potential that does not interrupt the required light amount even if there is a change with time or an environmental change.

The charging current of the charging charger 2 is set to be larger than that of the other charging devices, and the charging current is applied to the outside of the image forming area. Therefore the non-image portion is an image forming area outside but is applied by a charger 2, without being exposed in the exposure unit 3, the surface potential (residual potential) V _R in the non-image area after light irradiation by an eraser 4 The potential can be detected by the potential sensor 16.

A fixed reference pattern 17 is provided on the scanning start end side of the contact glass 10, and the reference pattern 17 is scanned before scanning the original.

FIG. 2 shows the time-dependent deterioration of the surface potential of the photoconductor in the latent image forming section. In FIG. 2, the image reflectance light amount shown on the horizontal axis indicates the image density reflectance placed on the contact glass 10, and is a value obtained by taking a relative value with the reflectance of the white portion as 100 as a scale. 20
0 indicates that the amount of light is twice that of the white part. The vertical axis indicates the surface potential (V) of the photosensitive drum 1.

The potential control reference pattern 17 has a density in which the first detection portion 17a has a light amount ratio of 1/100 of the white portion reflectance, which is substantially the same as that of the black portion of the image. The second detection portion 17b has a density having the same light amount ratio as the white portion reflectance 100, that is, the same density as the white portion. That is, the first detection portion 17a is a black pattern, and the second detection portion 17b is a white pattern.

First detection by the post-exposure potential sensor 16 for detecting partial serving Kurobe pattern 17a potential V _D and the second detection portion serving white part pattern 17
The potential _VL detected by the post-exposure potential sensor 16 in b changes with time. In FIG. 2, in the early stage of the photoconductor,
V _R at time photoreceptor has passed the curve A and a time showing a V _R
The curve B indicates that the initial detection potential V _Da of the black portion pattern 17a is about 800 V, but at a certain point in time, the temporal detection potential V _Db is reduced to, for example, 700 V due to a change with time. This change is caused by the change over time of the photoconductor and the charger. The initial detection potential V _La of the white portion pattern 17b is 150V, whereas the temporal detection potential V _Lb has increased to, for example, 320V. This is due to the change over time of the photoconductor and the exposure lamp.

The residual potential V _{R on the} surface of the photoconductor after cleaning the reference pattern of the photoconductor and static elimination by the static elimination lamp 9 is obtained by setting the light quantity of the static elimination lamp 9 to 250, that is, 2.
Assuming that the light amount is five times, the initial residual potential V _Ra is, for example, about 5 V (ideally 0 V), whereas the temporal residual potential V _Rb
Rises to, for example, 85V. This involves changes with time of the photoconductor and the static elimination lamp, but most of them are caused by deterioration of the sensitivity of the photoconductor due to light fatigue, and the surface potential does not attenuate.

Here, the difference V _D -V _L of the obtained stable latent image in the photosensitive drum 1 and the detection potential V _L of the detection potential V _D and white portions of the black portion
Needs to be constant.

Residual potential V _R of the photosensitive member surface as described above can not be constant over time, increase in residual potential V _R due to fatigue of the photoreceptor can not be avoided. Considering the change of the residual potential V _R, how well it is possible to make constant the V _D -V _L as a photosensitive body is fatigue, it is possible to stabilize the latent image. That is, as shown in FIG. 3, with respect to the curve A showing the initial state, the residual detection voltage V _R of the photosensitive member in the aging curve B obtained by correcting the Kurobe detection potential V _D and white portion detected potential V _L can get. The charge amount and the exposure amount are controlled according to the curve B. According to the curve B, the transition of the potential between the dark part and the light part is substantially the same as the initial state shown in the curve A.

To explain an embodiment of the control, in the initial stage, the black pattern 17a and the white pattern 17b on the contact glass 10
The charge amount and the exposure amount are controlled by the potential sensor 16 so that the detection potential becomes 800 V and 100 V, respectively. That is, by controlling the grid voltage of the charging charger 2, the detection potential of the black portion pattern is controlled to be 800 V, and the exposure lamp is controlled.
By adjusting the voltage of 11, the detection potential of the white portion pattern is controlled to be 100V. If the machine and the photoconductor are new, the offset amount of the developing bias voltage is adjusted to be ideally zero. This is called initial setting.

Hereinafter, the control will be described based on the flowchart shown in FIG. The machine is controlled under default settings. It is determined whether the copy enable state within 5 seconds when the ON of the machine main switch, if Yes, the until then V _D control signal corresponding to the V _R value of is issued. If NO, a high voltage is applied to the charging charger 2, the eraser 4 and the neutralizing lamp 9 are all turned on, and the photosensitive drum 1 rotates. After one rotation of the photosensitive drum 1, and inputs a voltage detected by the potential sensor 16 to the control system as V _R. For example, if the input signal is V _R = 100V, the signal is applied a developing bias voltage V _B to the developing bias control unit to 100V weighted. The detected voltage data 100V of the potential sensor is sent to the control system as a shift amount determination condition when determining a control value for controlling the exposure lamp 11 and the charging grid voltage. In the control system, weighting the data 100V new residual potential V _R to the potential V _R which is set before.

After data input, control is performed according to the sequence of the main unit. At the time of copying, the machine starts up according to the main body sequence. At this time, the black part detection potential V _D and the white part detection potential
It is determined whether or not from the detection of the V _L becomes 50 th, the signal detected by the potential sensor 16 as long as NO is ignored, the current state of charge charger grid voltage V _C and the exposure lamp voltage V _LP is applied Is done.

If the number is 50, and if Yes, the detection values of the potentials of the black pattern and the white pattern by the potential sensor 16 are input to the control system.

V _D control voltage, for example - is obtained by {sensed voltage (800 V + V _R value)} / 1.1, when V _R is 0V Kurobe potential V _D is 850V (850-800) /1.1=45V next, which point Is controlled to a voltage obtained by subtracting 45 V from the charging charger grid voltage V _{C in the} above. V _D is 700V and V _R is 5
When 0V is controlled to {700- (800 + 50)} / 1.1 = -136V and the voltage obtained by adding the 136V to the charging charger grid voltage V _C at that time.

On the other hand, V _L control voltage, for example - provided by {(100 V + V _R value) detected voltage} / 3, when V _R is 0V at a potential V _L of the white portion is 70V (100-70) / 3 = 10V next 10 V with respect to the exposure lamp voltage V _LP at that time
Is controlled to a voltage obtained by subtracting. If V _L is 200 V and V _R is 50 V, then {(100 + 50) −200} / 3 = −17 V, which is 17 V with respect to the exposure lamp voltage V _LP at that time.
Is controlled to a voltage obtained by adding.

The change to each value to be controlled can be performed sequentially after the detection, but the case where all of V _R , V _D , and V _L are detected and fed back at the time of the next copy image formation after the detection is shown.

When Kurobe potential V _D and white portion potential V _L is not detected, but it is of course charges by eraser 4 is erased, the detection timing from the amount of variation of the machine and the photosensitive member may be so set arbitrarily .

Can also be the user for the image quality adjustment to be able to arbitrarily set the developing bias voltage V _B, the actual development bias voltage value V _B in that case, (default value)
+ A (set value by the user) + (weighted voltage by V _R detected value). Needless to say, in the above example, the settings set by the user are excluded.

An example of performing V _R detected only when the main switch is ON is shown above may be performed after the copying is complete.

The process of fatigue of the photoreceptor includes fatigue due to charging in addition to fatigue due to light. Depending on the amount of electric charge applied to the photoreceptor, for example, the residual potential V _R increases earlier and increases more as the amount increases. So by measuring the post-charging applied using a large becomes a charger for most charge amount, of the machine, for example, an optimum controllable for the worst V _R variation of the replication system. The amount of charge passing through the photoreceptor is proportional to the value of the current flowing through the photoreceptor in FIG. 1, but in practice, an aluminum drum is placed at the position of the photoreceptor and the current flowing through the aluminum drum is substituted. As a result of the measurement for each charger, the amount of charge passed by the charging shears is the largest.

The degree of fatigue of the photoreceptor is indicated by the residual potential V _{R. In} this case, the potential is indicated by the potential of a portion that has been charged once and then removed by the eraser once. Take. Further, it is a lower limit potential that does not become lower than the amount even if the amount of charge removal is increased. In this sense, the white portion at the end of the image is irradiated twice with the exposure and the eraser, so that the degree of fatigue is not reduced by the potential of this portion.

Since the degree of fatigue of the photoreceptor does not change significantly for each copy, the potential of the reference pattern is used for density detection and other purposes.
V _D, there is no need to detect frequently as when detecting the V _L. Moreover, only the photoreceptor motor, static elimination lamp, charging charger and eraser are operated for a few seconds to detect the degree of fatigue, so there is no particular noise, no discomfort to the user, and a large time loss if copying is not in progress. As a result, there is no major problem in fatigue detection. Measurement of the surface potential of the photosensitive member V _R is as an example using the rising time of the fixing unit when the main switch ON, the need may be carried out in one or another suitable time when the machine end of use, whereas V _D, the detection of V _L is frequently Te, but different because previous history effect of the photosensitive member, it is better to detect every copy in some cases.

The effect present invention, always latent image potential V _D of the black portion and the white portion, the difference between V _L (V _D -V _L) be constant is maintained, the latent image in the linear region can be obtained , A stable latent image is obtained,
Copy quality is also improved. For example, excellent image quality can be obtained without deterioration in sharpness, reproducibility of a low contrast portion, gradation, and the like. Since the present invention the latent image potential of the reference pattern white portion higher than the residual potential V _R of the photosensitive member potential is set by, the fatigue state, such as the sensitivity of the photosensitive member is not deteriorated also to increase the light amount of the exposure lamp Since there is no lamp, there is an advantage that the image quality is good and the life of the lamp is not shortened. This extends the life of the machine and the life of the photoconductor.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an embodiment of an image forming apparatus to which the present invention is applied, FIG. 2 is a diagram showing a potential characteristic of a latent image forming portion due to fatigue of a photoconductor, and FIG. 3 is a residual potential of the photoconductor. FIG. 4 is a potential characteristic diagram of the latent image forming portion of the photosensitive member corrected according to FIG. 4, and FIG. 4 is a control flowchart according to the present invention. DESCRIPTION OF SYMBOLS 1 ... Photoreceptor drum, 2 ... Charger 3 ... Exposure part, 4 ... Eraser 5 ... Developing part, 9 ... Static elimination lamp 10 ... Contact glass, 16 ... Potential sensor 17 ... Reference pattern

Claims (4)

(57) [Claims] A method for controlling an image forming apparatus having means for forming an electrostatic latent image according to image information on a photoreceptor and developing means for visualizing the electrostatic latent image; Detecting the latent image potential of each of the color portions of the reference latent image having the black portion and the white portion, and detecting the residual potential of the photoconductor; and detecting the latent potential of each of the black portion and the white portion. A target potential is set based on the initial latent image potential of the black portion and the detected residual potential, and the detected latent image potential of the black portion is moved to the target potential so that the difference in image potential becomes a predetermined constant value. As described above, and based on the initial latent image potential of the white portion and the detected residual potential, the amount of shift from the initial latent image potential of the black portion to the target potential is the same as the shift amount from the initial latent image potential of the white portion. The shifted second target potential is set, and the detected white portion Method of controlling an image forming apparatus and controls the electrostatic latent image forming means to move the image potential on the second target potential. 2. The control method according to claim 1, wherein a developing bias voltage is controlled based on the detected residual potential. 3. A method for detecting a latent image potential in each color portion of a reference latent image having a black portion and a white portion formed on a photoconductor, and detecting a residual potential of the photoconductor. The developing bias voltage is controlled based on the difference between the initial residual potential and the detected residual potential so that the difference between the latent image potentials of the black part and the white part becomes a predetermined constant value. The amount of charge and the amount of exposure on the photoreceptor are controlled based on the difference between the initial latent image potential of the portion and the detected black latent image potential and the difference between the initial latent image potential of the white portion and the detected white latent image potential, respectively. A method for controlling an image forming apparatus, comprising: 4. A control method for an image forming apparatus, comprising: forming an electrostatic latent image corresponding to image information on a photosensitive member and visualizing the electrostatic latent image to form an image; Detecting potentials; detecting latent image potentials at respective densities of a reference latent image having a black portion and a white portion formed on the photoreceptor; increasing the detected residual potential from the previous detection Controlling the developing bias voltage so as to superimpose an applied voltage, and increasing the residual potential and initializing the black portion so that the difference between the latent image potentials of the black portion and the white portion becomes a predetermined constant value. An image characterized by controlling a charging grid voltage and an exposure lamp voltage based on a difference between a latent image potential and a detected black latent image potential and a difference between an initial latent image potential of a white portion and a detected white latent image potential. A method for controlling a forming apparatus.